U.S. Pat. No. 5,252,370 and U.S. Pat. No. 5,334,433 disclose a write-once optical recording medium having a recording layer containing an inorganic compound, i.e. silver oxide or iron nitride. Upon exposure to recording laser light, an inorganic compound in the recording layer decomposes to release a gas, creating a space in the recording layer. A recess is created on the substrate surface or the reflective layer due to the pressure of evolving gas. The space and recess cause a change of optical conditions, resulting in a substantial lowering of reflectivity where the laser light is irradiated. This enables reproduction in accordance with the CD standard.